This invention relates to a solid propellant rocket motor which is fundamentally of the end-burning type but has the capability of considerably increasing its thrust at a desired stage of its operation.
A principal characteristic of solid propellant rocket motors of the end-burning type is the ability of maintaining a practically constant but relatively low level of thrust for a relatively long period of time. Accordingly rocket motors of this type exhibit their utmost merit when used for propulsion of relatively low speed projectiles that need to be steered during flight.
A drawback of end-burning type solid propellant rockets is unstableness of the trajectory during an initial stage of flight immediately after launching by reason of lowness of the initial velocity. As an effective remedy for this drawback, it is known to bore an axial hole in an aft end portion of the end-burning propellant grain to provide an interior burning surface which intersects the primary burning surface at the aft end of the grain to thereby increase the rate of gas generation or mass burning rate, and hence the thrust of the rocket motor at an intial stage of operation.
However, an inherently low level thrust of an end-burning type solid propellant rocket motor offers another problem to a projectile propelled by this rocket motor even at a later stage of the flight. That is, when it is desired to steer the flying rocket projectile so as to achive a relatively large deflection of the flight course, the smallness of the thrust of the rocket motor offers a rather strict limitation on the degree of allowable deflection, and therefore it is not always possible to change the flight course as greatly as and as quickly as desired.